已知地球半径R=6.4×106m，地面附近重力加速度g=9.8m/s2，一颗卫星_爱下问搜题

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问题问答题

已知地球半径R=6.4×10⁶m，地面附近重力加速度g=9.8m/s²，一颗卫星在离地面高为h=3.4×10⁶m的圆形轨道上做匀速圆周运动．求：

（1）卫星运动的线速度．

（2）卫星的周期．

答案

（1）在地面附近有：G

Mm

R2

=mg ①

在离地面h高处轨道上有：G

Mm

(R+h)2

=m

v2

R+h

②

由 ①②联立得v=

gR2

R+h

=6.4×10³m/s

（2）由 m(

2π

T

)2(R+h)=m

v2

R+h

得：

T=

2π(R+h)

v

带入数据得：T=9.62×10³s

答：（1）卫星运动的线速度为6.4×10³m/s；

（2）卫星的周期为9.62×10³s．

完形填空

Life in the 22^nd century will be different from that in the 21^st century because many changes will happen in the new century. 1_____ what will the changes be?
First, the population is growing very fast. There 2      more and more people in the world and most of them will live longer than before. Computers will be 3     smaller and more useful, and there will be 4     one in every home. And 5      studies will be one of the most important subjects in schools.
Second, people will work 6      hours than they are doing in the 21^st century. They’ll have more free time for sports, watching TV and7    . Traveling will also be cheaper and easier. And more people will go to8      countries for holidays.
Third, there will be changes in our food, too. People will use more land to 9      new towns and houses. Then there will be less room for cows and sheep, so 10       will be more expensive. Maybe no one eat it everyday; 11     , they will eat more vegetables and fruit. Maybe people will be 12     .
Last, work in the future will be13      , too. Robots will do the 14     and hard work. Because of this, many people won’t have 15     work to do. This will be a problem.

C．no more than

选择题

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